184 PLANT ORGANS OR PARTS OF PLANTS. 



The odor of the fresh leaves is pecuHar and disagreeable ; 

 they possess a slight tea-like aroma. In infusion they 

 develop the original disagreeable odor. The taste is 

 acrid and bitter. 



Histology. — The upper epidermis of elongated polyg- 

 onal cells, with sometimes slightly undulating walls, 

 bears here and there simple and glandular hairs, but no 

 stomata. The simple hairs are long, two to four-celled, 

 very thin-walled, the terminal cell bluntly pointed. They 

 show an inclination to turn at the cell-joinings. Often, 

 too, the walls of a single cell are collapsed, while those on 

 either side retain their normal form. The glandular 

 hairs are short, formed of a one or two-celled pedicle 

 supporting a spherical one or two-celled head, containing 

 a yellow resinous mass. The mesophyll consists of a 

 single row of palisade cells and three or four rows of 

 thin- walled, round or elongated parenchyma, loosely 

 arranged, with large intercellular spaces. Calcium oxa- 

 late crystals are entirely absent. The structure of the vas- 

 cular bundle in the primary nerve is bi-convex, formed 

 of radial rows of vascular tissue and a sieve portion, 

 separated by masses of polygonal, vertically elongated, 

 and densely thickened wood tissue. Large-celled paren- 

 chyma and interlocked collenchyma occupy the space 

 between the fibro-vascular bundle and the epidermis 

 on either side. The under epidermis is composed of 

 unusually small cells with undulating interlocking out- 

 lines. Both varieties of hairs are plentiful. The stomata 

 are also of frequent occurrence. They are small, oval, or 

 often almost round. 



Powder. — The most conspicuous element of the powder 

 is the hairs. These, with their extremely thin walls, 

 are of diagnostic importance. Portions of the un- 

 der epidermis, with their small interlocked cells and 

 stomata, are also noteworthy. For the rest, the fibro- 

 vascular elements and parenchyma are of little value. 



